Layered metal phosphonate , structure

Zinc benzenesulfonate, Zn(C6H5S03)2,6H20, is prepared in aqueous solution and has a structure containing alternate layers of [Zn(H20)6]21 and benzenesulfonate ions. They can be compared to layered metal phosphonates 43... 

Figure 9 Schematic structure of layered metal phosphonate phosphonates with interlayer hydrogen-bonding.

Poojary D. M., Zhang B. and Clearfield A., Pillared layered metal phosphonates. Syntheses and X-ray powder structures of copper and zinc alkylenebis(phosphonates). J. Am. Chem. Soc. 119 (1997) pp. 12550. 

Metal phosphonates are usually prepared by reaction of phosphonic acids with metal salts under hydrothermd conditions [5-7]. Layered structures are predominant for most metals, the organic group being oriented more or... 

Layered structures are also common in trivalent metal phosphonates [16-18], and practically the sole ones in tetravalent metal phosphonates. Most metal IV phosphonates, such as Zr(03PPh)2 [19, 20], present a structure in which the metal atom is coordinated to six different phosphonate groups through the oxygen atoms. 

Layered metal IV phosphonates are widely used, particularly zirconium phosphonates, because their synthesis is versatile and their structural arrangement may be tailored to applications. Zirconium phosphonates are usually prepared by heating an aqueous solution of a metal IV salt (e.g., ZrOCl2) with a phosphonic acid at 60-80 °C synthesis in the presence of HP permits one to increase significantly the crystallinity of the final products. 

Zinc [37], manganese [38], molybdenum [34], and vanadium [40,41] also form lamellar structures. For example, molybdenyl phenylphosphonate forms a linear structure with double chains in which the molybdenyl oxygens of the adjacent chains point toward each other and the phenyl groups are on the outside [42], As is the case with zirconium phosphate and phosphonate, the layered nature of the above metal phosphonates is similar to that of the respective phosphates. Among these, vanadium phosphonates have generated greater interest in view of their importance as industrial catalysts. 

The metal phosphonate compounds usually adopt layered or pillared layered structures with the organic moieties filling in the inter-layer spaces [1-4]. The layered nature makes them interesting candidates to host intercalation reactions. Furthermore, the potential for the organic moieties to be modified by functional groups allows for the preparation of a number of new materials that have possible applications in areas such as catalysis, ion exchange, sensing and ion conduction [1,4-7]. 

In certain cases, self-assembly methods can be employed to prepare multilayered thin films analogous to LB films. Typically, once the surface has been primed with a molecular adhesion layer, subsequent layers are assembled in a layer-by-layer fashion where the end group of the previously deposited layer directs the assembly of the next layer. Strong electrostatic or covalent interactions between the layers serve to stabilize the assemblies. The most notable examples of self-assembled multilayered films are those based upon metal phosphonates [21]. Although these multilayers are structurally analogous to LB films, their thermal and solvent stability makes them potentially more useful in many applications, including electron-transfer studies. 

Lamellar or linear structures are also formed by various other metal ions, such as zinc, (268) manganese, (269) molybdenum, (270) and vanadium (271,272). Among these other solids, vanadium derivatives attracted significant attention due to their potential as industrial catalysts. The structures of the metal phosphonates are similar to those of the corresponding phosphates, in a manner similar to the zirconium phosphate/phosphonates. Polymerization of phenylphosphonate, for example, with Mo(IV) resulted in a linear double-stranded structure where the phenyl groups are positioned on the outside of the linear structure (273). These other metal derivatives are bound to yield many future investigations regarding the fundamental and applied chemistry of layered materials. 

Tetravalent metal phosphonates, or MELS (for Molecularly Engineered Layered Structures), provide a novel class of materials that combine many of the properties of incn-ganic metal oxides with the organic functionality more commonly found in functionalized polymeric resins. Early development work on these materials was carried out by Alberti and co-woikers [ref. 1] and Dines et al. [ref. 2]. Synthesis and characterization of related zirconium phosphates that also contain phosphonate groups as pillars have been described by Clearfield [ref 3]. There is a substantial patent estate for tetravalent metal phosphonates, and exclusive rights to this estate are owned by Catalytica [ref 4]. 

Multilayers of Diphosphates. One way to find surface reactions that may lead to the formation of SAMs is to look for reactions that result in an insoluble salt. This is the case for phosphate monolayers, based on their highly insoluble salts with tetravalent transition metal ions. In these salts, the phosphates form layer structures, one OH group sticking to either side. Thus, replacing the OH with an alkyl chain to form the alkyl phosphonic acid was expected to result in a bilayer structure with alkyl chains extending from both sides of the metal phosphate sheet (335). When zirconium (TV) is used the distance between next neighbor alkyl chains is 0.53 nm, which forces either chain disorder or chain tilt so that VDW attractive interactions can be reestablished. 

Amino-carboxylic and phosphonic acids are known to form open frameworks (i.e. porous materials), particularly with first-row transition metal ions. Lanthanide diphosphonates with 3D pillared-layer structure are also known and several classes of ligands such as sim-... 

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